Re: [Xen-users] Ram Calculation

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Mon, Dec 21, 2009 at 4:01 AM, ShaunR <mailinglists@xxxxxxxxxxxxxxxx> wrote:
> Years ago when i first started using xen i specified a dom0_mem=xxx in grub.
>  I no longer do this

why?

>, what i do now is set the dom0_min-mem setting in
> xend-config.sxp to 1024

it provides two different things. The grub line sets the initial dom0
memory, while xend-config sets the minimum dom0 memory.

>.  I also have a few scripts that run at boot and one
> of them does a `xm mem-set 0 1024`.  after that a xm list 0 shows dom0
> allocated 1024 Ram.

Without grub.conf line, this essentially do a ballon-down of dom0
memory. It's different from setting dom0_mem in grub.conf in that this
method :
- allows dom0 memory to be ballooned-up later
- uses up a portion of dom0 memory to maintain the necessary memory
structure to be ballooned-up, thus can be a waste of (some) memory.

>  The problem comes on teh system when i run free or free
> -m, free shows dom0 using 1336096 with only 1160512 used.  This also
> prevents the other command i run `xm mem-max 0 1024` from running correctly.
>  Anybody know if this is a bug or what may be going on here.  Is there
> anyway to force dom0 to 1024 with out having to specify it in grub?

Not sure what you mean. In essence, I recommend you use dom0_mem.

>
> Next problem is the mem usage from xm info.  xm info shows the host having a
> total of 32766 Ram, and a free memory of 12531.  when i do a xm list and
> total the ram for all running domains (including dom0) it doesn't come out
> to 12531.  How can i get accurate reporting of how much ram the system has,
> how much each guest is really using, and how much ram is really free?

My best guess is that xen itself uses some amount of memory for each
running domU. Thus the sum of memory of all running domUs from "xm
list" is lower compared to (total_memory - free_memory) from "xm
info".

-- 
Fajar

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